Ratio and Proportion Formulas

The ratio of two quantities a and b in the same units, is the fraction and we write it as a : b.In the ratio a : b, we call a as the first term or antecedent and b, the second term or consequent. Eg. The ratio 5 : 9 represents with antecedent = 5, consequent = 9.Rule: The multiplication or division of each term of a ratio by the same non-zero number does not affect the ratio.Eg. 4 : 5 = 8 : 10 = 12 : 15. Also, 4 : 6 = 2 : 3.

2.Proportion:

The equality of two ratios is called proportion.If a : b = c : d, we write a : b :: c : d and we say that a, b, c, d are in proportion.Here a and d are called extremes, while b and c are called mean terms.Product of means = Product of extremes.Thus, a : b :: c : d ⇔ (b x c) = (a x d).

3.Fourth Proportional:

If a : b = c : d, then d is called the fourth proportional to a, b, c.Third Proportional:a : b = c : d, then c is called the third proportion to a and b.Mean Proportional:Mean proportional between a and b is ab.